<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        p{
            /*font-size必须要有单位*/
            font-size: 16px;
        }
    </style>
</head>
<body>
    <p>字体大小</p>
    <div>字体大小</div>
</body>
</html>